Strip-shaped lamina and laminated stator core for an electric machine

ABSTRACT

A strip-shaped lamella ( 10 ) for a stator ( 30 ) of an electric machine, having a yoke region ( 12 ) and a number of first teeth ( 18 ) that are of one piece with the yoke region ( 12 ) on a first side ( 14 ) and have first grooves ( 20 ) between them, and having second teeth ( 22 ) that are of one piece with the yoke region ( 12 ) on a second side ( 16 ) oriented away from the first side ( 14 ) and have second grooves ( 24 ) between them. The second teeth ( 22 ) are located at a position of the first teeth ( 18 ).

PRIOR ART

The invention relates to a strip-shaped lamella for a stator of anelectric machine as well as a laminated stator core comprised of suchstrip-shaped lamellas. The German patent application DE-OS 26 29 532 hasalready disclosed a stator for an electric machine that is comprised ofa yoke packet, which is initially flat in form. To that end,strip-shaped lamellas provided with grooves are disposed so that theyform a flat lamella packet. All of the grooves of the individuallamellas are oriented in the same direction, thus lending this packetthe appearance of a comb. This packet, which is intrinsically flat, willbe referred to below as a flat packet. In a subsequent step, this flatpacket is rolled into a round shape, yielding laminated stator core thatcan be used in the same way as conventional annular laminated statorcores.

In a first exemplary embodiment, the prior art has disclosed a flatpacket, the back of which, oriented away from its teeth, is providedwith grooves designed to function as preferred folding points. Theintent is to produce a cylindrical surface with a polygonal base, thecorners of the polygon being constituted by the axes of the grooves. Inanother exemplary embodiment, the prior art has disclosed a flat packetthat has a groove behind each of the teeth that are later orientedtoward the rotor. Both laminated stator cores share the common traitthat the round-rolled flat packets, despite being to a large extentround, are not only relatively strongly polygonal in form, but alsosimultaneously have relatively strong undulations of the lamellas. Theseundulations have a powerful negative effect, more or less, on theproperties of the flat packet and round packet. Above a particular yokeheight, the deformations are so great that the necessary shape andposition tolerances of the packet become impermissibly pronounced.

ADVANTAGES OF THE INVENTION

The strip-shaped lamella according to present invention, with thecharacteristics of the main claim, has the advantage that its locationof the second teeth in a position of the first teeth results in arelatively long, unnarrowed cross section of the yoke and/or yoke regionand consequently achieves a very favorable degree of roundness of theround-rolled strip-shaped lamellas and of the laminated stator corecomposed of such strip-shaped lamellas. Bending points that reduceroundness are largely avoided. In order to achieve a favorableefficiency between the finished stator and the rotor, it is necessary tohave a high degree of roundness and therefore a small gap that is asuniform as possible between the stator and rotor. The steps proposedaccording to present invention render it unnecessary to subsequentlymachine the inside of the stator, which makes the proposed stepseconomically significant. The bending results and therefore theroundness of the stator require a groove bottom between each pair offirst teeth to extend essentially in a straight line.

A particularly favorable bending result is achieved if the groove bottombetween each pair of first teeth extends in a straight line over atleast 50% of its length in the first approximation. In the secondapproximation, a value of at least 60% is preferable. It is particularlypreferable for this value to lie between 60% and 70%.

Another increase in the quality of the bending results is achieved inthat the groove bottom between each pair of second teeth also extendsessentially in a straight line; a further increase in the quality isachieved if the shorter of the two respectively opposing groove bottoms,with reference to the longer straight section, extends in a straightline over at least 80% of its length. It is particularly preferable forthis value to lie between 80% and 93%.

If a stator manufactured with such strip-shaped lamellas is to besupported in a housing by means of the so-called axial clampingtechnique, then it is necessary for the stator to have a certain amountof axial clamping surface. To that end, the second groove has thenarrowest cross section possible or, stated in reverse, the second teethdo in fact have the largest possible cross-sectional area, but there isa relatively small transition surface between the second teeth and theyoke region. The second groove is correspondingly embodied astrapezoidal or T-shaped. A favorable degree of roundness of theround-rolled strip-shaped lamellas and/or laminated stator core can alsobe achieved if a groove lying between two second teeth has a generallyround form, for example oval or also circular.

The present invention also relates to a laminated stator core for anelectric machine that is manufactured out of the lamellas according tothe invention. A laminated stator core of this kind has a particularlyfavorable degree of roundness and can also be produced with only slightaxial tolerances. This increases the precision with which the laminatedstator core fits into a housing of an electric machine. This alsoincreases the cooling of the stator due to the increased surface area.

In addition, an outward-facing side of the second teeth has a radiusthat is smaller than the radius of the stator. A convex shape of thesecond teeth offers a flat packet stator advantages with regard to roundrolling, machining, and lacquering. It also facilitates insertion into abearing shield.

The stamped concave form produces a punctiform and/or linear contactsurface for the bending roller or the bending tool. This sharply reducesthe friction during the bending process so that the bending occurs moreeasily and therefore more gently for the tool and the work piece.

For example, if the end surface of the radially outer edge of the statormust be machined so that a bevel or a radial insertion aid is produced,then an externally rounded tooth results in narrower cutting anglesbetween the cutting tool and the outer tooth. This improves chipformation and reduces burr formation in the exit region of the tool.

The round contour of the outer teeth improves lacquer quality bypreventing paint buildup and flow fractures during lacquering.

Due to the concave design of the teeth, the housing shield rests againsteach tooth at only one point when assembled.

Furthermore, the laminated stator core, composed of the lamellasaccording to the present invention, has at least one end lamella withsecond teeth that have an axial end surface that transitions into thenon-axial outer contour of the second teeth by means of a roundedtransition. Also with such an outer contour of the lamellas and endlamellas, a cutting surface of a cutting tool, for example a lathechisel, cuts into the work piece at a very flat angle, for examplebetween 30 and 45°. This also significantly improves chip formation andextends the life of the tool edge considerably. It also facilitatesinsertion into the bearing shield and improves machining in the axialdirection.

The present invention also relates to an electrical machine with alaminated stator core that is composed of the lamellas according to thepresent invention. This electrical machine has an improved efficiency.Moreover, the particularly favorable degree of roundness of thelaminated stator core reduces stress in the housing parts since theloads that the laminated stator core exerts on the housing parts are nowdistributed over a larger area, thus permitting the housing parts to beoptimized in terms of their strength. The housing parts are lessvoluminous and therefore lighter in weight.

DRAWINGS

The drawings represent exemplary embodiments of a strip-shaped lamellaaccording to the present invention, a laminated stator core, and anelectric machine.

FIG. 1 shows a detail from a side view of a first exemplary embodimentof a lamella according to the present invention,

FIG. 2 shows a side view of a second exemplary embodiment of a lamellaaccording to the present invention,

FIG. 3 shows a side view of a third exemplary embodiment of astrip-shaped lamella,

FIG. 4 shows a side view of a fourth exemplary embodiment of astrip-shaped lamella,

FIG. 5 shows an enlarged detail of a yoke region between two first andsecond teeth,

FIG. 6 shows a detail of a stator composed of lamellas according to thefirst exemplary embodiment,

FIG. 7 shows a detail of another exemplary embodiment of a stator,

FIG. 8 shows a detail of a third exemplary embodiment of a stator,

FIGS. 9 to 13 show side views of the stator yoke and the outer teeth,

FIG. 14 shows an end lamella with a rounded transition from the endsurface to the outside of the outer teeth,

FIG. 15 symbolically depicts an electric machine.

DESCRIPTION OF THE EXEMPLARY EMBODIMENTS

FIG. 1 shows a detail of a first exemplary embodiment of a strip-shapedlamella 10. The lamella 10 has a yoke region 12 that extends over theentire length of the lamella 10. The yoke region 12 has a first side 14and a second side 16. The first side 14 has first teeth 18 protrudingfrom it, with first grooves 20 between them. On the second side 16opposite from the first side 14, there are second teeth 22, which are ofone piece with the yoke region 12 and the first teeth 18. Second grooves24 extend between the second teeth 22. With regard to the yoke region12, an axis can be established that extends through the yoke region 12from left to right in FIG. 1. With regard to the first teeth 18 and thesecond teeth 22 in connection with this axis, it can be ascertained thatthe second teeth 22 are located at a position of the first teeth 18. Asis true of all of the exemplary embodiments for the lamellas 10, thestrip-shaped lamella 10 is intended to start in a state in which theyoke region extends in a straight line and then be curved into a roundform, producing an on the whole annular arrangement of each individual,originally straight, strip-shaped lamella 10. Each strip-shaped lamella10, together with other lamellas that form a stack, is rounded so thatthe first teeth 18 extend toward a radial inside of a finished stator orround-rolled strip-shaped lamella. The second teeth 22 then pointradially outward. In this first exemplary embodiment, the first grooves20 and the second grooves 24 are each embodied as slightly trapezoidal,the shorter parallel side of one such trapezoid being constituted by theradial outside of the yoke region 12. The first grooves 20 are roundedat the corners, i.e. at the transitions from the second teeth 22 to thesecond side of the yoke region 12. In the exemplary embodiment accordingto FIG. 1, the first grooves 20 and the second grooves 24 have the samegroove contour starting respectively from the first side 14 and thesecond side 16 of the yoke region 12; the first groove 20 is larger andtherefore naturally deviates from the groove contour of the secondgroove 24 starting from a length that corresponds to that of the secondgroove 24. The half-sized second tooth 22 indicated with dot-and-dashlines is optional. For space reasons, regardless of the dimensions thefirst and second teeth and regardless of their association to oneanother, at least one screw shaft S is positioned in the grooves 24 whenthe electric machine is assembled and serves to clamp a stator composedof the lamellas 10 by means of at least two housing parts.

In the exemplary embodiment according to FIG. 2, the lamella 10 isprovided with a different outer contour, i.e. with different secondteeth 22. When it undergoes round rolling, the strip-shaped lamella 10in the exemplary embodiment according to FIG. 2 behaves in precisely thesame way as the one shown in FIG. 1. The difference between the twoexemplary embodiments lies in the fact that the second teeth 22 of thesecond exemplary embodiment have a larger surface area in the axialdirection, i.e. as shown in the depiction according to FIG. 2. Aclamping force acting in the axial direction on the stator installed ina generator housing thus acts on the enlarged second teeth 22. It isthus possible to increase the clamping force and decrease the load onthe teeth 22. In the exemplary embodiment according to FIG. 2, thesecond groove 24 is trapezoidal.

The exemplary embodiment according to FIG. 3 shows an embodiment of thelamella 10 that is further optimized in terms of the load exerted byaxial clamping forces, in which the second grooves 24 have only aT-shape.

FIG. 3 a shows a variant of the second teeth that is optimized in termsof the bending deformation on the outside of the yoke region 12 thatoccurs while the flat packet is being rounded. The second teeth 22 shownhere have an approximately central indentation 25 so that the secondteeth 22 deform only slightly and the rigidity of the flat packetconsequently remains largely intact for the axial clamping of the statorin the housing.

In the exemplary embodiment according to FIG. 4, the second grooves 24are generally round in shape. This generally round shape can be an ovalshape, a circular shape, or a semicircular shape as depicted in FIG. 4.

In FIG. 5, the geometry of the first grooves 20 and second grooves 24 inthe yoke region 12 are explained in detail. In the first grooves 20, twodimensions are of particular initial interest. The first dimension b₁represents the width of the first groove 20, which is determined bytheoretically extending the tooth flanks of the first groove 20 untilthey intersect with the imaginary extension of the first side 14. Thedistance between these two intersection points is the starting value.The second dimension in the first grooves 20 is the dimension b₂, whichcorresponds to the perfectly straight portion at the groove bottom of agroove 20. A groove bottom 26 extends between each pair of first teeth18, essentially in a straight line at first. In addition, the groovebottom 26 between each pair of first teeth 18 extends in straight linefor at least 50% of its length. The minimum value of 50% corresponds toa ratio of b₂ to b₁.

In addition, with regard to the second teeth 22 and with regard to thegroove bottom 28 between two second teeth, this groove bottom alsoextends in an essentially straight line. The width b₃ is determined in amanner analogous to that of the width b₁; the width b₄ is determined ina manner analogous to that of the width b₂. The ratio between b₄ and b₃is advantageously such that the groove bottom 28 between each pair ofsecond teeth 22 extends in a straight line for at least 65% of itslength.

A favorable value for the ratio between b₂ and b₁ has turned out to beroughly 65%.

An analogously favorable ratio between b₄ and b₃ lies between 60% and85%, or even better, between 60% and 75%. The best ratio has turned outto lie in the range between 63% and 71%.

FIG. 6 shows a detail of a stator 30 comprised of lamellas 10 accordingto the exemplary embodiment shown in FIG. 1. The stator 30 has secondteeth 22 on its outer circumference that transmit the correspondingaxial force exerted by the intrinsically known axial clamping technique.

FIG. 7 also shows a stator 30. By contrast with the exemplary embodimentaccording to FIG. 6, though, the stator 30 has lamellas according to thepresent invention only in a central region. These lamellas 10 dolikewise serve to absorb axial forces, but are also used forimplementing the intrinsically known center lamella clamping technique.In the axial direction to the right and left of the center lamellas inthe stator 30 described here, there are lamellas without second teeth 22so that their outer circumference is essentially cylindrical. FIG. 8depicts an exemplary embodiment of another stator 30 in which only everyother first tooth 18 is associated with a second tooth 22.

FIG. 9 shows that the outer diameter Da of a stator 30 also includes theentire length of the second teeth 22. For technical reasons related tothe bending process, the second teeth 22 are provided with a particulardesign on the radial outside of the teeth 22 so as to induce the leastamount of friction possible between a bending tool and the outside ofthe strip-shaped laminated stator core while the strip-shaped laminatedstator core is in the process of being bent. In an exemplary embodimentaccording to FIG. 10, the radially outer contour of the second tooth 22has a radius R on the order of half the diameter Da. Preferably, theradius is shorter than the radius of the stator 30.

According to the exemplary embodiment shown in FIG. 11, the radiallyouter contour has a radius R on the order of roughly 50 to 60% theperipheral width of a second tooth 22; the radius is therefore muchshorter than the radius of the stator 30.

According to the exemplary embodiment shown in FIG. 12, the radiallyouter contour has a radius R that continually decreases in length thefurther it is from the outer diameter Da, finally transitioning into thelateral tooth flanks with a radius R of roughly 15 to 30% the peripheralwidth of the second tooth 22. The outer diameter Da is greater than R1and R1 is greater than R2. An advantageous value range for the radius Rhas turned out to be between 1.5 mm and 10 mm.

Optionally, the outer corners of the second teeth 22 can be radially andaxially beveled in relation to the stator, FIG. 13, or a statorinsertion aid can be lathed onto them, i.e. they can be lathed down to acylinder, to facilitate insertion of the stator into an opening of ahousing in which the stator is to be accommodated.

The smaller an angle a enclosed between the radially outer contour and abevel edge 53 being provided, the more favorable the chip flow whenbeveling by means of a cutting tool 50. In addition, this also improvesburr formation.

Rounded edges on the second teeth 22 also improve the lacquering qualitysince considerably less paint buildup occurs.

FIG. 14 shows a detail of a laminated stator core 30 that is composed ofthe lamellas according to the present invention, which has at least oneend lamella with second teeth 22 that have an axial end surface thattransitions into the non-axial outer contour of the second teeth 22 bymeans of a rounded transition. This shape can be produced, for example,by being stamped onto the outer lamella strip of the flat packet, beforeor after packeting. The rounding is preferably provided on the radialoutside of the outer teeth, but also on the peripheral sides of theteeth. In addition, the contour of the first teeth 18 is also rounded,thus making it possible to avoid damaging inserted windings,particularly while the laminated stator core is being rounded.

FIG. 15 shows an electric machine 40 that has a stator 30 or a laminatedstator core comprised of the lamellas 10 according to the presentinvention.

The laminated stator core comprised of the lamellas 10 according to thepresent invention, i.e. the previously mentioned flat packet, isprovided with a stator winding before being rolled round and the coilsides of this stator winding are accommodated completely inside thefirst grooves 20 before the round rolling is carried out. Thedisposition of the coil sides depends on the winding design.

1. A strip-shaped lamella for a stator of an electrical machine,comprising a yoke region; a number of first teeth that are of one piecewith said yoke region on a first side of said yoke region and havingfirst grooves between said first teeth; second teeth that are of onepiece with said yoke region and are located at a position of said firstteeth on a second side of said yoke region oriented away from said firstside and having second grooves between said second teeth, said secondteeth having a width b4 which corresponds to a perfectly straightportion of a groove bottom and a width b3 which corresponds to adistance between two intersecting points, said intersecting points beingdetermined by theoretically extending tooth flanks of said second grooveso that they intersect with imaginary extensions of said groove bottom,and a ratio between the widths b4 and b3 is between 60% and 85%.
 2. Astrip-shaped lamella as defined in claim 1, wherein said groove bottombetween each pair of said first teeth extends substantially in astraight line.
 3. A strip-shaped lamella as defined in claim 2, whereinsaid groove bottom between each pair of said first teeth extends in astraight line for at least 50% of its length.
 4. A strip-shaped lamellaas defined in claim 2, wherein said groove bottom between each pair ofsaid second teeth extends in a straight line for at least 65% of itslength.
 5. A strip-shaped lamella as defined in claim 1, wherein each ofsaid second grooves has a shape selected from the group consisting of atrapezoidal shape and a T shape.
 6. A strip-shaped lamella as defined inclaim 1, wherein an outward facing side of each of said second teeth hasa radius that is shorter than a radius of the stator.
 7. A laminatedstator core for an electrical machine, comprising a plurality ofstrip-shaped lamellas, each of said lamellas having a yoke region, anumber of first teeth that are of one piece with said yoke region on afirst side of said yoke region and having first grooves between saidfirst teeth; second teeth that are of one piece with said yoke regionand are located at a position of said first teeth on a second side ofsaid yoke region oriented away from said first side and having secondgrooves between said second teeth, said second teeth having a width b4which corresponds to a perfectly straight portion of a groove bottom anda width b3 which corresponds to a distance between two intersectingpoints, said intersecting points being determined by theoreticallyextending tooth flanks of said second groove so that they intersect withimaginary extensions of said groove bottom, and a ratio between thewidths b4 and b3 is between 60% and 85%.
 8. A laminated stator core asdefined in claim 7; and further comprising at least one end lamella withsaid second teeth that have an axial end surface that transitions into anon-axial outer contour of said second teeth by a rounded transition. 9.An electrical machine, comprising a laminated stator core composed atleast partially of a plurality of strip-shaped lamellas, each of saidlamellas having a yoke region; a number of first teeth that are of onepiece with said yoke region on a first side of said yoke region andhaving first grooves between said first teeth; second teeth that are ofone piece with said yoke region and are located at a position of saidfirst teeth on a second side of said yoke region oriented away from saidfirst side and having second grooves between said second teeth, saidsecond teeth having a width b4 which corresponds to a perfectly straightportion of a groove bottom and a width b3 between which corresponds to adistance between two intersecting points, said intersecting points beingdetermined by theoretically extending tooth flanks of said second grooveso that they intersect with imaginary extensions of said groove bottom,and a ratio between the widths b4 and b3 is between 60% and 85%.